RFR: 8184777: Factor out species generation logic from BoundMethodHandle

[Claes Redestad]

Hi,

  this patch factors out the BoundMethodHandle species data class
generation to a new ClassSpecializer facility.

  While currently semantically neutral, this will make it possible
to reuse the facility in other places.

  Webrev: http://cr.openjdk.java.net/~redestad/8184777/open.00/
  Bug: https://bugs.openjdk.java.net/browse/JDK-8184777

  Performance wise this adds a very small (~20k bytecode) amount
of work to the initialization costs of BMHs, which we expect will
be more than repaid as we apply the ClassSpecializer elsewhere.

  Thanks!

/Claes